AOAC Methods for Review in Codex STAN 234_11-2018

AOAC Official Methods Listed in CXS 234 for Milk and Milk Products

70

2.6.01

( h ) Other standard solutions. —Dilute aliquots of solutions ( b ), ( c ), and ( e )–( g ) with 0.5M HCl to make ³ 4 standard solutions of each element within range of determination. C. Preparation of Test Solutions ( Caution: See Appendix B , safety notes on wet oxidation, hydrofluoric acid, and perchloric acid.) ( a ) Inorganic materials and mixed fertilizers. —Dissolve 1.00 g well-ground test portion in 10 mL HCl in 150 mL beaker. Boil and evaporate solution nearly to dryness on hot plate. Do not bake residue. Redissolve residue in 20 mL 2M HCl, boiling gently if necessary. Filter through fast paper into 100 mL volumetric flask, washing paper and residue thoroughly with H 2 O. Measure absorbance of solution directly, or dilute with 0.5M HCl to obtain solutions within ranges of instrument. If Ca is to be determined, add enough La stock solution to make final dilution 1%La (i.e., 5 mLLa to 25 mL flask, 20 mL to 100 mL flask, etc.). ( b ) Fertilizers containing organic matter ( tankage, corncobs, cottonseed hulls, etc. ).—Place 1.00 g test portion in 150 mL beaker (Pyrex, or equivalent). Char on hot plate and ignite 1 h at 500°Cwith muffle door propped open to allow free access of air. Break up cake with stirring rod and dissolve in 10 mL HCl as in ( a ). ( c ) Fertilizers containing fritted trace elements.— Dissolve £ 1.00 g well-ground test portion in 5 mL HClO 4 and 5 mL HF. Boil and evaporate to dense HClO 4 fumes. Dilute carefully with H 2 O, filter, and proceed as in ( a ). Alternatively, dissolve test portion in 10 mL HCl, 5 mL HF, and 10 mL methanol. Evaporate to dryness. Add 5 mLHCl and evaporate. Repeat HCl addition and evaporation. Dissolve residue as in ( a ). (Normally Pt ware should be used; Pyrex or other glassware may be used if Na, K, Ca, and Fe are not to be determined.) ( d ) For manganese.— ( 1 ) Acid-soluble, for both Mn 2+ and Mn 4+ .— See ( a )–( c ) and 972.02 ( b ) ( see 2.6.22). ( 2 ) Acid-soluble, for Mn 2+ only.—See 972.02 ( a ) ( see 2.6.22), 940.02 ( see 2.6.23), and 941.02 ( see 2.6.24) . ( 3 ) Water-soluble, for Mn 2+ only.—See 972.03 ( see 2.6.25). ( e ) For iron and zinc. —( 1 ) Aqueous extraction. —Place 1.00 g test portion in 250 mL beaker, add 75 mL H 2 O, and boil 30 min. Filter into 100 mLvolumetric flask, washing paper with H 2 O. Dilute t o vo l ume a nd r e d i l u t e i f n e c e s s a r y. ( 2 ) Ch e l a t i on extraction. —Place 1.00 g test portion in 250 mL beaker, and add 5 cm (2 in.) magnetic stirrer bar and 100 mL 2.5% EDTA solution (w/v). Stir exactly 5 min, and filter through Whatman No. 41 paper,

AOAC Official Method 965.09 Nutrients (Minor) in Fertilizers Atomic Absorption Spectrophotometric Method

First Action 1965 Final Action 1969

AOAC–AACC Method

A. Apparatus and Reagent ( a ) Atomic absorption spectrophotometer. —Several commercial models are available. Since each design is somewhat different, with varying requirements of light source, burner flow rate, and detector sensitivity, only general outline of operating parameters is given in Table 965.09 . Settings and procedures must be adapted to specific apparatus with table used only as guide to concentration ranges and flame conditions. ( b ) Disodium EDTA solution. —2.5%. Dissolve 25 g Na 2 H 2 EDTA in 1 L H 2 O and adjust to pH 7.0 with 5M NaOH, using pH meter. B. Standard Solutions (Do not use <2 mLpipets or <25 mLvolumetric flasks. Automatic dilution apparatus may be used. Prepare standard solutions in 0–20 m g range fresh daily.) ( a ) Calcium solutions. —( 1 ) Stock solution. —25 m g Ca/mL. Dissolve 1.249 g CaCO 3 in minimum amount 3MHCl. Dilute to 1 L. Dilute 50 mL to 1 L. ( 2 ) Working standard solutions .—0, 5, 10, 15, and 20 m g Ca/mLcontaining 1%La. To 25 mLvolumetric flasks add 0, 5, 10, 15, and 20 mL Ca stock solution. Add 5 mL La stock solution and dilute to 25 mL. ( b ) Copper stock solution. —1000 m g Cu/mL. Dissolve 1.000 g pure Cu metal in minimum amount HNO 3 and add 5 mL HCl. Evaporate almost to dryness and dilute to 1 L with 0.1M HCl. ( c ) Iron stock solution. —1000 m g Fe/mL. Dissolve 1.000 g pure Fe wire in ca 30 mL 6M HCl with boiling. Dilute to 1 L. ( d ) Lanthanum stock solution. —50 g La/L. Dissolve 58.65 g La 2 O 3 in 250 mL HCl, adding acid slowly. Dilute to 1 L. ( e ) Magnesium stock solution. —1000 m g Mg/mL. Place 1.000 g pure Mg metal in 50 mL H 2 O and slowly add 10 mL HCl. Dilute to 1 L. ( f ) Manganese stock solution. —1000 m g Mn/mL. Dissolve 1.582 g MnO 2 in ca 30 mL 6MHCl. Boil to remove Cl 2 and dilute to 1 L. ( g ) Zinc stock solution. —1000 m g Zn/mL. Dissolve 1.000 g pure Zn metal in ca 10 mL 6M HCl. Dilute to 1 L.

Table 965.09. Operating parameters Element Wavelength, Å

Flame

Range, m g/mL

Remarks

Ca

4227 4227 3247 2483 2852 2795 2138

Rich Air–C 2

H 2

2–20 2–20 2–20 2–20

1% La, 1% HCl

Rich N 2

O–C 2

H 2

Requires special burner

Cu Fe Mg Mn Zn

Air–C 2

H 2

Rich Air–C 2 Rich Air–C 2

H 2 H 2

0.2–2

May need La

Air–C 2 Air–C 2

H 2 H 2

2–20

0.5–5

ã 2005 AOAC INTERNATIONAL

10/9/2018